Spark plug



K. c. DE WALT SPARK PLUG Filed Aug. 1, 1936 Inverwtor: Kenneth C. DeWal by Hwyaf wl Hls Attorneg.

Jan. 11, 1938;

Patented Jan. 11, 1938 UNITED STATES 2,105,411 SPARK PLUG Kenneth C. De Walt, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application August 1, was, Serial No. 93,855 4 Claims. (c1. 1zs 1e9 The present invention comprises an improved spark plug for internal combustion engines.

Heretoi'ore it has been common practice to insulate from one another the oppositely charged parts of a spark plug by an elongated insulator commonly consisting of porcelain. The central conductor is threaded through the insulator which is mechanically clamped by a screw threaded member within the casing of the plug. It is well known that some disadvantages accompany such a construction. For'example, the end of the insulator is subject to carbon deposition from the combustion mixture and theinsulator sometimes is cracked by the compressive 35 forces to which it is subjected, when it consists oi opaque material, such as porcelain, the light irom the spark cannot be seen from the exterior and hence the operativeness of the spark plug cannot be ascertained by observing light emitted u by the plug.

In accordance with the present invention all such difiiculties are absent and a convenient structure is provided by making part or the shell or outer member of a spark plug oi glass which is integrally united or welded to adjoining metal parts. No other insulator need be provided between the sparking conductors. An internal conductor is joined to a metal portion of the shell at the endof the plug which is remote from the location 01 the terminals between which the spark occurs. If partial obscuration of the light emitted by the spark can be tolerated, a battle is provided between the sparking terminals and the glass insulator, thereby preventing deposition of U carbon or other conductive material upon the inner surface of theinsulator.

The accompanying drawing shows in Fig. 1 a longitudinal section of a preferred form of spark plug embodying my invention; Figs. 2 and 3 are longitudinal sections of modifications; and Fig. 4

is a perspective enlarged view of a bailie and support employed in the modification of Fig.

Referring to Fig. 1, the spark plug illustrated consists of an elongated shell or housing made up of a heavy-walled metal body portion i, a

. glass portion '2, and a relatively thin-walled metal cap portion 3. An interior conductor 4 is attached at one end to the cap portion 8 of the shell. It terminates at the opposite in a sparking tip I, which as illustrated, may have a smaller cross section than the main portion of the conductor l. The sparking tip I cooperates with a similar sparking tip 8 projecting from the screwthreaded portion 1 of the plug which is constructed to engage with an opening in the wall of an engine cylinder. The attached end 01' the conductor 4 is grooved at 8 and is firmly gripped by the cap 3, which engages with the groove.

The body portion I terminates at the end 0pposite the spark tip 6 in a lip 9 of reduced thick 5 ness which preferably tapers down to an even smaller rim. The opposite rims of the glass cylinder 2 are sealed by fusion to the rim of the lip 9 and the rim of the cap 3. The seals between the glass and the metal members are maintained 1 strain-free by so choosing the glass and metal that the thermal expansion characteristics of the glass and metal are substantially coincident at temperatures below the zone of transformation temperatures of the glass, that is, at the zone of temperature at which the thermal expansion characteristics rapidly increase with temperature. Such a seal is described in a copending application, Serial No. 705,250, filed January 4, 1934 by E. E. Burger and A. W. Hull (see corresponding French Patent 784,164 issued April 23, 1935). This seal also is described in an article by A. W. Hull and E. E. Burger in Physics, Vol. 5, No. 12, pages 384-411. As there explained, a suitable strain-free seal may be made by sealing a hard glass, sold in the open market by the Corning Glass Co. of Corning under the name Corning Gill, to metal members having suitable thermal expansion characteristics, for example, an alloy consisting oi 54 per cent iron, 28 per cent nickel and 18 per cent cobalt. The above application and article describes various equivalents for this particular glass and this particular metal alloy.

If desired, the member 1 may be constructed of two parts brazed or otherwise joined to another, the thick walled part in consisting of iron 0 or other inexpensive metal and the lip 5 consisting of alloy suitable for joining to glass.

In the spark plug shown in Fig. 1, the space between theinner conductor 4 and the outer shell is unobscured so that light from the spark between-the tips 5 and 6 may be seen through the glass member 2. The condition of the spark thus may be observed and the condition of the plug thus may be determined, without the necessity of using special testing appliances or removing the plug.

Inthe modification shown in Fig. 2, the metal 'bafile ii is mounted upon the inner conductor 4,

the walls of the shell i being somewhat cut away as indicated at H. Particles of metal, carbon,

or other conducting material can only reach the inner surface of the glass window 2 through a sinuous elongated path. Hence the amount of such deposition will be greatly decreased. The

battle H, as indicated, consists of a cylindrical portion and an outwardly extending radial portion, the former making frictional engagement with the conductor i.

In the modification shown in Fig. 3, the bailie l4 consists of an insulating .rnateii'al such as alumina, magnesia, porcelain or silica. It is shown somewhat enlarged in Fig. 4 together with the holder i5 whereby it is mounted upon the conductor E. The support 15 makes a frictional engagement, both with battle H and the con ductor The segmental members l5a may be bent outwardly to engage firmly and positively with the baille H. r

What I claim as new and desire to secure by casing consisting of a plurality of metal members and an intermediate hollow cylindrical glass member which is sealed at opposite ends to said respective metal members and a cooperating conductor sealed to one of said members and extending in sparking relation to another of said metal members.

3. A spark plug for internal combustion apparatus comprising the combination of a hollow casing consisting of a metal base, a cap and a glass insulator which is fusion-sealed to said base and cap, a conductor sealed to said cap and projecting through said casing and a baille mounted on said conductor.

4. A spark plug comprising the combination of a massive, hollow metal base constructed to engage with an engine cylinder well, said base having a rim of reduced thickness, a hollow glass cylinder sealed at one rim thereof to said base rim, 2. cap closing the opposite rim of said glass cylinder and being fusion-sealed thereto, a conductor extending from said base, and a second conductor joined to said cap, projecting longitudinally through said casing and extending in sparking relation to said base conductor.

KENNETH C. DE WALT. 

